1. Field of the Invention
The present invention relates to preparation of polyphenylene ether, and more particularly to a process for producing polyphenylene ether to improve safety and yield thereof.
2. Description of Related Art
Polyphenylene ether (PPE) is a polymer mainly contained of benzene rings and formed by benzene molecules and oxygen atoms combined with ether linkages. PPE has good thermal and mechanical stability, and its coefficients of thermal expansion, formation compressibility and creep as well as water absorption are all low. These properties contribute to excellent processability and formability. PPE also possesses outstanding electrical properties due to its low dielectric loss and good insulating quality. Over wide ranges of temperature, frequency and humidity, its dielectric constant and dissipation factor almost remain unchanged, so PPE has great dielectric performance.
Conventionally, polyphenylene ether (PPE) is made by oxidizing and polymerizing carbon atoms and oxygen atoms of 2,6-dimethylphenol (2,6-DMP) and oxygen (O2) in the presence of an organic solvent and a coordination complex catalyst formed by copper and amine. Additionally, when 2,6-DMP is co-polymerized with a phenolic compound having functional groups, a desired modification of 2,6-DMP can be achieved to further improve PPE's property. For example, 2,6-DMP and a bisphenol can be co-polymerized to form a bisphenol-modified 2,6-DMP at its two terminals having OH functional groups, wherein the bisphenol is tetramethylbisphenol-A (TMBPA), tetramethylbisphenol-F (TMBPF), tetramethylbiphenol (TMBP) or 4-bromo-2,6-dimethylphenol (BDMP). Alternatively, 2,6-DMP can be co-polymerized with alkenyl phenol to form an alkenyl phenol-modified 2,6-DMP that has alkenyl functional groups, wherein the alkenyl phenol is 2-allyl-6-methylphenol (AMP) or 2-butenyl-6-methylphenol (BMP).
The reaction for forming PPE has to be performed in the presence of oxygen, an organic solvent such as toluene or alcohol solvent and a catalyst. Therein, o oxygen is known as a combustion-supporting gas or agent, and the organic solvent is a combustible material, while the processing equipment tends to produce static electricity, which acts as an igniter. In other words, the conventional PPE preparation involves all three essentials of combustion, i.e. a combustion-supporting agent, a combustible material and an igniter. If the process is not properly designed, the reaction for producing PPE is very dangerous and highly explosive.
For prevention of explosion, a known approach controls the combustible organic solvent kept its gaseous concentration below the minimums of explosion thereof to eliminate explosive factors associated with the combustible. Additionally, the reaction equipment of producing PPE is mainly designed to prevent from generation of static electricity (i.e. the igniter).
However, for gain a high yield of PPE, pure oxygen or oxygen regarded as a combustion-supporting agent is used at a high concentration even going beyond the limiting oxygen concentration (abbreviated as LOC) of relative reaction solvent thereof. Accordingly, the whole process for producing PPE still has a persistent risk factor from the combustion-supporting agent thereof.
As shown in FIG. 1, in a known oxidation polymerization process for producing PPE (abbreviated as PPE-producing process), an apparatus implemented has an oxidation-polymerization reactor 10, provided therein with a traditional impeller mixing device 20. The impeller mixing device 20 uses a rotatory shaft 21 to drive vanes 22 at the terminal of the rotatory shaft 21 to rotate and thereby stir a solution of PPE (abbreviated as PPE reactant) 30. While the vanes 22 rotate, an oxygen nozzle 60 immersed in the PPE reactant 30 may introduce a high-pressure oxygen gas into the PPE reactant 30, so that the rotating vanes 22 promote the contact between oxygen gas and the PPE reactant 30, making the PPE reactant 30 get an oxidation polymerization in the presence of the oxygen gas and a catalyst, thereby obtaining the desired PPE.
Since the supplied oxygen is not effectively contacted with the PPE reactant 30, and the catalyst in use is a copper-amine complex, water is generated during process for producing the PPE and degrades the reaction. Consequently, the resultant PPE yield is too low to support industrial manufacturing. Especially, for preventing explosion, the whole PPE-producing process is performed under a low-oxygen condition, which brings further limitation to the PPE yield. Besides, the traditional impeller mixing device 20 uses a mechanical seal on the rotatory shaft 21, and tends to cause leakage of oxygen and generation of static electricity, making the production of PPE highly dangerous.